1. Field of the Invention
This invention relates to an improved system for restraining a vehicle such as a transport truck or trailer which is to be restrained from movement at a loading dock. This invention is also related to a sensing system for use with such a vehicle restraint.
2. Prior Art
A variety of techniques are known by which a vehicle is mechanically secured to prevent movement by using the ICC bar as the means to engage the truck or trailer. U.S. Pat. No. 4,127,856 Bickel describes the use of electrical switches to sense the engagement of the vehicle restraint with a bar mounted on the rear of a vehicle. The commercial use of locking devices is now well known in the art. For example, the Rite-Hite "Dok-Lok", Serco "VR" and Kelley "Truk Stop" and "Star" all have models that contact a vehicle ICC bar and constrain the truck from movement. Models of those systems generate signals to indicate that engagement has occurred so that personnel at the loading dock have an audible/visual indication of locking.
These techniques are mentioned or described in many U.S. Patents including, U.S. Pat. Nos. 4,267,748; 4,282,621; 4,488,325; 4,553,895; 4,692,755; 4,695,216; 4,759,678; 4,830,563; 4,843,373; 4,938,647; and 4,946,330.
One characteristic of previous ICC bar engagement devices is that the system had limits of engagement known as an "operating envelop". The ICC bar, by previous Governmental regulation could not be higher than 30 inches off the ground. This formed the upper limit of the operating envelop. The lower limit is not defined by regulation but determined as a function of trailer manufacturer (as is the case of the shape of the ICC barrier itself) and the degree of float of the truck as it is loaded and unloaded. Typically the lower limit was approximately 15 inches. Consequently, the operating envelop required that the vehicle restraint not only capture the ICC bar within that range but also have the ability to follow vertical movement as the vehicle "floated" during loading operations to maintain engagement. Moreover, the restraint has to lower and disengage from the ICC bar when the bar itself is at the lower end of the envelop or else the vehicle will remain constrained while loaded and ready to depart from the dock.
Contemporary designs for trailers are lowering the ICC bar clearance from the ground to about 10 inches. Prior systems due to mechanical configuration cannot operate within an envelop from 10 to 30 inches. The configuration of the devices even in the lowermost position project above 10 inches, whether track mounted or surface mounted. This will not allow them to engage, restrain and disengage a vehicle ICC within the totality of the contemporary operating envelop.
Thus a need currently exists for a vehicle restraint having the desirable characteristics of commercial devices but with an extended operating range.
Systems in use have electrical switches which generate a signal by the presence or absence of physical contact with a moving part. A switch senses a change in the position of a component of the restraining device. The switch does not directly sense the presence or absence of the bar mounted on the rear of a vehicle. While such systems generally function well, and provide useful information to the control system, there are two major deficiencies in all of the previous systems. First, the loading dock area and the rear end of trailers can be very harsh environment as a result of rain, snow, ice, road salt and other materials present at a loading dock. These devices use mechanical limit switches which have moving parts which can become corroded or made inoperative by ice, dirt or other debris. Even if the limit switch is an inductive proximity switch, it is still activated by the motion of a mechanical component of the restraining device, and are therefore is subject to malfunction or false signal if one of the moving components should become broken or stick from corrosion or other foreign matter. Consequently a need still exists in the art for improved sensing techniques, especially as the operating range of the restraint increases.